1. Field of the Invention
The present invention relates to a gearbox with coaxial drive and driven shafts, wherein a clutch sleeve which can be displaced in the axial direction of these shafts can be moved from a coupling position in which the drive and driven shafts directly connected into a position in which the shafts are connected at least by one gear stage.
2. The Prior Art
The use of different motors for different numbers of revolutions has already been known in conjunction with the cutting of hard rocks. Thus, for example, it has already been suggested to change over from a fast-running electric motor to a slowly running hydraulic motor, in which case, however, when changing over to the slower cutting speed only a reduced output of the hydraulic motor could be made use of. However, a high cutting capacity is required even at lower cutting speeds, especially when cutting hard rocks, which capacities cannot be achieved with slowly running hydraulic motors.
As a rule, gearboxes known so far have relatively large dimensions and consequently, especially when high torques have to be transmitted, the entire jib geometry had to be modified, since such a gearbox cannot be used in existing designs without problems.
A gearbox with a short construction, which is constructed as a multi-path gearbox with torque equalisation, is known already, for example, from German patent 2 419 673. In this known construction a clutch sleeve, displaceable in the axial direction of the coaxial drive and driven shafts, is provided, which in a central position reaches a disengaged position. In one of the displaced positions of the clutch sleeve the input and output shafts are connected directly with each other. In any case, due to its construction the clutch sleeve is engaged with the respective gears only over a relatively short axial length and, for the purpose of transmitting greater torques, this design requires a greater axial overall dimension. Moreover, in the case of this known construction a relatively more expensive mounting is required for the intermediate shafts and the individual parts of the transmission, as well as for the drive and driven shafts.